This invention relates to an algorithm for estimation of parameters for an optimum power level for a write process in a CD-RW OPC operation.
In a CD-RW OPC procedure for writing information on a CD-RW disk, it is desirable, if not necessary, to determine an optimum power level for the write process. Reference power level and other parameters are provided for by the CD-RW disk manufacturers as part of the ATIP (Absolute Time In Pregroove) information. In order to estimate optimum power, several frames are written in the PCA (Program Calibration Area), using different laser power settings that are selected according to the reference power level value(s) provided. The written frames are then read back, using read power, by measuring reflected power I11 and theoretical maximum power Itop for each frame and estimating the modulation amplitude as
m=I11/Itop.xe2x80x83xe2x80x83(1)
The calculated value m will vary with the power level P, and a smooth curve is fitted to the values of m calculated for each applied power level P. From the fitted curve of m versus P, a normalized slope xcex3, defined as
xcex3(P)=d(ln{m(P)})/d(ln{P}),xe2x80x83xe2x80x83(2)
is computed and used to estimate a power P whose corresponding slope value xcex3(P) is closest to the known slope value for the present target, provided by the disk manufacturer.
Because of the nature of the firmware, complex calculations of the values for xcex3(P) must often be avoided. What is needed is a method of estimating a curve for the modulation amplitude m(P) and for the normalized slope xcex3(P) that determines relevant curve parameters using relatively few measured data values and using only a few computations, but is relatively robust against statistical fluctuations in data measurements.
These needs are met by the invention that, in one embodiment, provides a three-step process for estimating parameters for a modulation amplitude curve m(P), using only simple arithmetic operations. In this embodiment, the modulation amplitude m(P) is estimated using a three-parameter function, namely m(P)=C+A/(B+P), and the values of the parameters A, B and C are estimated using physical arguments and measured data values. The ultimate form of the modulation amplitude m(P) in this embodiment becomes m(P)=1xe2x88x92A{A+(Pxe2x88x92P0)}xe2x88x921, where P0 is a minimum power level value. below which the laser power is insufficient to set down a xe2x80x9cmarkxe2x80x9d on the CD-RW disk and A is an adjustment parameter used to approximate one or more measured data values.